Drafting styli and material therefor



April 1, 1969 H. w. FERCHLAND ETA L 3,435,528 DRAFTING STYLI ANDMATERIAL THEREFOR- Filed Dec. 6, 1966 DRAFTING A? MACHINE #L fig? ! l II I I I 1 .1 E y W y W W Ff INVENTORS Ware/a llfizrJ/azzd flqyzzsi/keJZh/hcqJ: w

ATTORNEY United States Patent 0.

DRAFTING STYLI AND MATERIAL THEREFOR Harold W. Ferchland, Troy, andAugustine J. Wallace,

Jr., Southfield, Mich, assignors to General Motors Corporation, Detroit,Mich., a corporation of Delaware Filed Dec. 6, 1966, Ser. No. 599,470Int. Cl. B431: 1/00 US. CI. 33-18 2 Claims ABSTRACT OF THE DISCLOSURE Adrafting stylus in the form of a thin pointed rod is composed of atin-nickel alloy in the ratio of approximately 65% tin and 35% nickel.

This invention relates to drafting styli and the composition thereof. Inthe automotive and aircraft industries it is necessary to produce veryaccurate drawings, for example, of body parts which may be directlyscaled or gauged to make dies and templates. It has become customary tomake these drawings upon a very stable material comprising a metal platecovered with seven layers of white paint. The drawings ordinarily havebeen executed by draftsmen using a gold alloy stylus sharpened to apaddle shaped point which will indent the paint to a prescribed depth,usually .003 inch, without cutting or scoring the paint and which willsimultaneously make a black line. These gold alloy styli however, erodeso rapidly that very frequent redressing of the point is necessary andin addition, when the line to be drawn changes direction as at a corneror a curve, the stylus must be manually indexed so that the longdimension of the stylus point will be in the direction of the stylusmovement.

With the advent of drafting machines, the gold alloy styli becameimpractical and a demand arose for a stylus which would require lessfrequent redressing and which would execute arcs of any radius or sharpcorners without indexing. Other requirements were that the line left bythe stylus must be erasable yet must be resistant to an ammonia solutionsince the drawings have to be cleaned by washing with an ammoniasolution. Further, because the drawings have to be reproducedphotographically, the lines produced on the plate must be indented inthe paint to help achieve proper lighting of the lines.

It is an object of this invention, therefore, to provide a material fora drafting stylus meeting all of the above requirements.

Another object of the invention is to provide a drafting stylus having aconfiguration and strength suitable for meeting the above requirements.

The invention is carried out by providing an alloy which when used in adrafting stylus will produce an erasable black mark resistant to anammonia solution. The alloy also has the characteristics to minimize theredressing requirements of the stylus.

The invention is further carried out by providing a stylus of atin-nickel alloy having a specific type of conical point.

The above and other advantages of the invention will become moreapparent from the following specification taken in conjunction with thedrawings in which;

FIGURE 1 is a schematic view of a drafting machine having a stylus, and;

FIGURE 2 is a side view of a drafting stylus according to the invention.

As represented in FIGURE 1 an automatic drafting machine includes astylus holder 12 for maneuvering and controlling a stylus 14.

It has been found that a suitable stylus for drafting machines of thetype described above is a thin rod 14,

Patented Apr. 1, 1969 as best shown in FIGURE 2, formed with a conicalpoint 16 wherein the included angle of the point is 60 to 90 and has asmall radius on the tip 18. The material of the stylus is a tin-nickelalloy.

The preferred composition of the stylus material is 65% tin and nickel.It has been found that this c0mposition is rather critical in that ifthe nickel content is made much higher the stylus becomes brittle andwill tend to break. On the other hand, if the tin content is madehigher, the alloy will be too soft so that an excessive wear rateresults which requires too frequent redressing. However, acceptableresults can be obtained when the tin-nickel alloy contains a proportionof tin in the range of 62% to 68%.

The stylus may be fabricated by casting or rolling metals of theprescribed composition. However, the preferred method of fabrication iselectro-plating where the alloy is deposited in a rod shape onto aconductive steel wire 20 from a plating solution having the followingcomposition: 49 g./l. SnCl 300 g./l. NiCl -6H O, 56 g./l. NH HF and, NHOH to raise pH to 2.0. The plating operation conditions are the same asthose given in Modern Electra-plating, second edition, by F. A.Lowenheim, 1963, p. 500.

Typical dimensions for a drafting stylus made by this method are a roddiameter of 0.072 inch and total length of 1.5 inches. The steel wire 20upon which the tin-nickel alloy is deposited is 0.032 inch in diameterand extends approximately one inch from the blunt end of the stylus. Thecone-shaped point '16 of the stylus includes a 60 angle and the extremetip 18 has a radius of 0.005 inch.

It has been found in practice that the stylus of this inventionsuccessfully meets the rigorous requirements set forth above. The devicehas sufficient structural strength to indent three layers of paint onthe drafting medium as is desired and leaves a fine uniform black linewhich is erasable and yet is resistant to a cleaning solution of onepart ammonia to five parts water. The angle of the point produces anindentation in the paint which enables superior photographicreproductions of the drawing to be made. It has also been found that thestylus has a much greater wear resistance than the previous gold alloy.

While the preferred embodiment of the invention is disclosed herein thescope of the invention is not limited thereto.

It is claimed:

1. A drafting stylus comprising a thin rod terminating in a conicalpoint defining an included angle in the range of 60 to 90, the rod beingcomposed of a material capable of producing an erasable black lineresistant to removal by an ammonia solution, the material comprising atinnickel alloy containing tin in the range of 62% to 68%.

2. A drafting stylus for a mechanical drafting machine comprising a thinrod terminating in a conical point defining an included angle in therange of to 90, the

stylus point being composed of a material capable of producing anerasable black line resistant to removal by an ammonia solutioncomprising an alloy of tin and 35% nickel.

References Cited UNITED STATES PATENTS 2,557,148 6/1951 Schimmel. 53,129,512 4/1964 Schiler.

3,192,630 7/1965 Dineson 33-138 X OTHER REFERENCES Publication:Metallurgia, Developments in the Met- 70 allurgy of Tin and its Alloys,December 153, pp. 277-281.

HARRY N. HAROIAN, Primary Examiner.

